Abstract
How does bright, chromatic illumination affect people’s ability to discriminate and name colours? Participants (n=22) viewed an IPS LCD screen next to a white RAL 000 90 00 sheet, each occupying 10° viewing angle, in an enclosed achromatic booth illuminated by tuneable multi-channel LED lamps (www.hi-led.eu). The display was surrounded by a hood to prevent light from the lamps falling on it. Following an initial 2-min adaptation period and training under D65 illumination, participants viewed on each trial: top-up D65 adaptation illumination (10 seconds); test illumination, under which they adjusted the chromaticity and luminance ofthe LCD screen to match that of the white sheet, using joystick buttons to navigate in CIELAB space; 11-point rating scale for confidence of their match; and a 12-choice colour naming question to describe the sheet colour. Matching durations on each trial were recorded but not constrained. In total, 6 saturated test illuminations with equal illuminance levels (red, green, blue, cyan, magenta, yellow) ranging from 67 ΔEab to 103 ΔEab from D65 and 3 daylight illuminations (“CCT”) (2650K daylight yellow, D65 white, 10000K daylight blue) were presented five times each inrandomized order. Results:Performance decreased with increasing saturation of the test illumination, from an average of 8.4 ΔEab chromaticity match (var 8.46) under D65 to 18.4 ΔEab (var 65.8) under the saturated blue illumination. On average, matches under saturated illuminations were 3 ΔEab worse than matches under CCT illuminations, although confidence ratings were higher for the former. Under CCT illuminations, the proportion of “white” sheet colour names increased with match duration. Under saturated blue, cyan and yellow illuminations, “white” colour names occurred on average after 102 seconds. White paper tends not to appear white under minutes-long exposure to coloured light, but people are able to match its colour.